Extra null check onReceive

- Fix NPE for `onReceive` with `null` extras
- Add some test for `onReceive` with `null` conditions
- Condition yoda remove
Deprecate G+ community in favor of StackOverflow.
Second pass based on feedback
- Refactor NetworkBroadcastReceiver for testing
- Refactor tests to actually test behaviour
- Introduce Util.getService cause long lines and everytime casting suck
Load video thumbnail if mimetype is video.
Rename verifyAirplaneMode to setAndVerifyAirplaneMode
Merge pull request #411 from eveliotc/extra-null-check

Extra null check onReceive
Thumbor does centerCrop

By default, such issue was closed.
Added test for centerCrop behaviour.
Remove centerCropRequestsAreNotTransformed as centerCrop requests must be transformed.
Merge pull request #428 from eveliotc/thumbor-does-centerCrop

Thumbor does centerCrop
Document empty path throws. File equivalent call.
Merge pull request #429 from square/jw/doc-tweak

Document empty path throws. File equivalent call.
Merge pull request #413 from square/dimitris/video

Load video thumbnail if mimetype is video.
Update javadoc.
Merge pull request #431 from square/dimitris/javadoccc

Update javadoc.
java8.
Merge pull request #432 from square/dimitris/ps

java8.
Use new string builder for fetch() requests
Merge pull request #442 from jfsso/master

Use new string builder for fetch() requests
Enforce main thread for api calls.
Revert "Enforce main thread for api calls."

This reverts commit 2e5625dbd88d312b6a642120defaf9cf2e8ec313.